Compressed gas regulators operate by reducing a high pressure gas through a variable orifice to a lower delivery pressure. As the pressure of the source drops, the regulator's control valve is automatically adjusted by a pressure sensing element to maintain a constant discharge pressure. The pressure sensing element can be a piston or a flexible diaphragm. Flexible diaphragms are generally preferred for low discharge pressures (less than 200 psig) because they provide more sensitive pressure control compared to pistons, which are rigid diaphragms, of equal area. In order to function adequately, a diaphragm must be thin enough to flex at the operating pressure of the regulator. This also means it must be highly stressed under normal operating conditions.
A major operational problem of flexible diaphragm regulators is rupture of the diaphragm, which can cause loss of the gas into the atmosphere. Diaphragms rupture for various reasons including: weakening caused by fatigue, buckling caused by overpressurization, loss of strength due to corrosion, or combustion when servicing an oxidant. Whatever the cause, a ruptured diaphragm results in the loss of pressure control as well as a discharge through the regulator's bonnet. This discharge is not a safety problem for ordinary inert gases, such as nitrogen, argon, or helium, provided that local ventilation is adequate to prevent asphyxiation. However, discharge of toxic, flammable, oxidizing or corrosive gases into the working area is extremely dangerous. Gases can also escape through the bonnet by leaking through the diaphragm seal. Although this type of discharge is slower than one caused by a diaphragm rupture, it still can be a safety problem for flammable or toxic gases.
A piston controlled regulator experiences less catastrophic failures than flexible diaphragm controlled regulators. A piston controlled regulator is essentially the same as a flexible diaphragm regulator except that the flexible diaphragm is replaced by a piston, which is a rigid type diaphragm. The piston moves in the regulator, rather than flexing, and has a dynamic seal, such as an o-ring, between it and the inside wall of the bonnet. While the piston, which is rigid, does not rupture, leaks can occur at the o-ring seal. Overall, the reliability of the piston is higher than the flexible diaphragm with respect to leaks into the bonnet. The major disadvantage of a piston controlled regulator is low sensitivity relative to flexible diaphragms of equal area. To compensate for this, a much larger piston diameter is required relative to a flexible diaphragm controlled regulator. This makes the piston controlled regulator large in size and more expensive than the flexible diaphragm controlled regulator.
Dome loaded regulators are also less subject to catastrophic failure in that they do not release gas upon diaphragm failure. However, they are inconvenient to use, are expensive, and have other hazards due to potential inadvertant downstream overpressurization. Some typical dome loaded regulators are shown in the following United States and French patents:
U.S. Pat. No. 2,158,068 to M. H. Grove, entitled "Gas Regulator, issued May 16, 1939;
U.S. Pat. No. 2,164,095 to F. E. Thomas, et al., entitled "Air-Pressure Reducing and Regulating Device," issued June 27, 1939;
U.S. Pat. No. 2,202,313 to M. H. Grove, entitled "Fluid Pressure Regulator", issued May 28, 1940;
U.S. Pat. No. 2,248,592 to L. W. Stettner, entitled "Pressure Regulator", issued July 8, 1941;
U.S. Pat. No. 3,437,110 to D. W. Birdwell, entitled "Fluid Pressure Relief Valve," issued Apr. 8, 1969; and
French No. 1,247,388 issued October 1960.
Therefore, it would be desirable to have a pressure regulator that would automatically shut off upon failure of the pressure sensing/control element so as to prevent release of any gas which can cause safety problems.